<HTML>I have been collecting information on pulse combustion ever since I ran across a service manual from Fulton Pulse combustion boilers written in 1991. Not enough information is available from any one source but it can be pieced together, slowly. They seem to be the most simple of devices, many with one or no moving parts and they are very efficient.

There are many designs of pulse combustion burners but the fall into two main catagories, single port or 2 port. In the 2 port it is basically a unaflow, with exhaust out one port and the fresh charge in the other. The single port or can is a counterflow burner and this design interests me with it's possible application to steam generation.

One of the biggest points for possable inefficiency in a high output automotive steam generator is the consumption of power and associated losses during the movement of air required for combustion. Jim Crank has mentioned the huge amount of electrical energy used in his land speed steamer more than once. Not only is conversion from steam to electricity to air flow a very inefficient path, but in a practical car, battery requirements become extreme during start up conditions and excess weight is another penalty they incurr. The pulse combustion burner uses power in the combustion to move the exhaust out and the fresh charge in for every cycle. It has less power needed for the pulse combustion furnace over most any other design because almost perfect combustion is automatically attained and no excess air is used. The power used to move the air of combustion goes through no energy transformations and experiences no associated losses. Further more, one ignition pulse starts the burner and then it is automatic in the regulation of the fuel and air of combustion. Adjusting the fuel flow will change the pulse rate and of course the heat output.

Burners of this type can opperate up to 200 pulses per second which makes each charge small allowing the charge to burn in a very short time. The small charges are burnt much quicker, providing for a very complete burn, and only a small combustion chamber is required, providing more than 5,000,000 BTU per square foot. As the number of pulses increases, the pressure in the burner also increases to as much as 3 atmospheres, pressures not usually attained in a boiler setting. A burner of this type increases it's possible heat transfer as it is pushed harder.

Noise is a consideration in pulse combustion but remember no one gave up on the Explosion motor because it made too much noise. Some pulse burners are like a siren and can be heard as far away as 6 miles, not what you want to hear going down the road. 2 Pulse burners paralleled, sharing the same ports will automatically achieve back and forth action that tends to cancel out the pressure waves.

Another interestinf feature is the fuel does not need to be vaporized or atomized for the combustion process. The fuel, even the heaviest oils if heated, are allowed to flow where the incoming air charge can draw them in. This makes the pulse burner require less energy than pump systems and safer than anything using highly flamable fuels in vaporizers or pressurized systems. The small combustion chamber does not allow a large build up of vapors or gasses that can lead to an explosion and an explosion is part of normal operation, including starting, anyway.

Speaking of fuel, the dreaded V-1, buzz bombs of WWII (the Argus-Schmidt tube engine, a 2 port pulse combustor) were successfully converted to burn coal dust when gasoline was not available by H. Wahl. After the war he produced a pulse gasification plant for coal dust that showed slag blows out properly and about 100 times greater furnace loading is possible than with ordanary coal dust burners.

This all sounds amazing to me, a burner that has a huge output for it's size, automatically adjusts to different fuels and burns almost perfectly clean, has no moving parts, is easy to fabricate, and requires little or no external handling of fuel or air for combustion.

Am I dreaming or are steamers just behind on this one ?

I look foward to discussing what might be a great jump in efficiency for the production of steam.

<HTML>Peter,
Neat stuff in all--it made me think immediately about the German pulse jets as you mentioned. One of the difficulties is that one great advantage of the external combustion engine is that the boiler firing has a relatively long time to completely burn the fuel and it makes me wonder if 200pulses per second would not result in the same problems as a very high speed gas engine---burn time in milliseconds with emission problems. Are you sure it burns almost perfectly clean? Certainly getting rid of air blower horsepower would be a good step forward.

Other later works have reached the same results of clean combustion and they claim absolutely no smoke from unburnt fuel at startup and shut down. The Fulton pulse combustion boilers I first noticed are used in homes and business across the country and they pulse at 39hz. With condensing exhausts they claim better than 95% efficiency. The ocillating pulses also improve heat transfer over steady state combustion.

The main reason that fuel burn takes time, is the need to expose the fuel to enough O2 for complete combustion. The pulse combustor has such ocillating turbulance and the entering air charge is accelerated beyond the speed which the fuel particles travel so they are continously scrubbed by fresh gasses. Also smaller fuel charges burn proportionatly faster than large charges, then we split 1 second of fuel release into 200 individual charges. Theroy shows pulses of 2000 per second should burn completly as I read through some papers.

The pulse rate can be varied in some pulse combustors as I have mentioned and it is linked to the amount of fuel available or the 1/4 wave resonant frequency of the device. In a short can type burner the resonant frequency is too high to be reached but with modifications to the size of the can and port it can be reached.

In keeping the exhaust clean, the fresh air entering the device doesn't mix in any way with exhaust, and the fresh air moves quickly enough to draw the fuel into the burner as the low pressure region is filled but the exhaust is too slow to provide the same effect.

<HTML>Peter,
Gaadzooks! Could you convert the heat transfer units t BTU/SQFT as I am still only 50% unpacked and would rather be out on my wonderful TREK bicycle(that I stole) oggling 70 year old women than search thru a bunch of boxes.
The only thing I am concerned about is Nitrous Oxides and that is not mentioned--high flame temperatures can create this. If this is nt a problem consider what kinds of heat transfer in a small space could be done with a forced circulated Lamont coil!
Best of New Years, George</HTML>

The noise problem could kill this. A scream heard 6 miles away indicates how bad they are in this regard. What could be done to make it just audible when standing nearby? I don't know what the db level for this would be but we need to set a standard for comparing all burners, including the howling classics that are also far too noisy.

<HTML>George,
All external combustion systems can be fine tuned to prevent NOx formation with the same methods as employed in the modern IC engine. The easiest way, and already in use in modern power plants also, is the recirculation of exhaust gasses. It is so much easier to implement with a burner than in an explosion engine and it moderates the temperature of the exhaust gasses in the boiler setting for less chance of overheating the superheater or reheater coils. The gasses are mostly inert and provide no support for combustion while preventing localized hot spots and peak temperatures that promote the NOx formation. I believe up to 50% exhaust gas recirculation has been used successfully in power plants. The overall heat transfer is unchanged but the transfer in individual sections of the boiler will change and design modifications may be needed.

I will convert the numbers for you when I get back home, using Suki's laptop at her place right now and I have no books around.

Graeme,

The Fulton pulse combustion boilers for home heating uses are very quiet but they are shrouded well and insulated, also they bolt them to the floor to help dampen the vibrations. As I said before, 2 pulse combustors operating in parallel with shared ports will automatically develop a alternating but synchronized combustion and the sound waves cancel each other out. A sound pressure level of 72 dB is very quiet for the operation of machinery and some recreational vehicles are held to this standard in the USA. I will look at the Fulton manual and let you know the ratings for their boilers.

<HTML>Bill,
As soon as I get to the work computer and remember the materials to copy, I will post some diagrams from patent drawings.

Warning:
Use Alcohol only !
Work outdoors with nothing flameable around you including your fuel can !
Wear a face mask and heat resistant gloves !
Have a working fire extinguisher close at hand !
Keep all spectators a safe distance away !
Do not try this experiment with modifications or other devices until you understand what you are doing !
Use your head and the common sense mother nature gave you !

If you want to play first, take a glass jam or mayonaise jar of about 3 inches in diameter and cut a smooth 1/2 inch hole in the lid. Pour about 1/4 inch of alcohol in the bottom, use dry gas or 91% rubbing alcohol, the 72% barely burns. Cover jar with the lid, be sure it is air tight around the seal, and then cover the hole in the lid with a finger and shake the jar to cover the walls with the alcohol. Next blow into the hole and mix the vapors with air, be sure there is no alcohol on the outside of the jar or lid and blow once more into the hole. Next introduce a flame to the hole being careful not to get your face or body in line with the hole as the first pulse blows flame outward. The remaining pulses show no visable flame outside the jar, but hot gasses will exit the hole and fresh air is alternately drawin in with rapid pulses. The jar will not explode but the heat will be much too intense for the glass and it should be stopped after a few seconds. After cooling it will easily start again but after a few runs the alochol will be depleated. This runs at about 20 cycles per second, far below the aproximate 200 hz of the jars fundimental frequency, far from resonance.

George,
A cyclone furnace, a standard in the modern power plant, has a velocity of 10 to 20 m/sec for the coal dust and supply air entering the burner and combustion is in the 0.1 second range. The pressure wave in a 0.75 meter long pulse combustor is around 300 m/sec and the coal dust may only enter at 10 m/sec. With the pulse going from 0 to 300 m/sec through the coal dust, twice, complete combustion is assured. This applies for liquid fuels as well but the liquid fuels start the trip at almost 0 m/sec. It is interesting to note that in pulse combustors that a laminar flow upon entry of fresh air, prevents the fuel from contacting the residual gasses and furnace walls so the wetting action familar with unburnt fuels and abrasive errosion from solids is non existant. The exhaust gasses are slower and shrouded by the incoming fresh charge so they have no abrasive action either. The longer the laminar flow continues in to the vessel, the longer the delay to ignition becomes, allowing larger charges. Ignition after the first pulse, is automatic and no spark is needed to continue the combustion process because the contact with residual gasses ignites the charge after the laminar flow becomes turbulant. This automatically prevents preignition, similar to that seen in an IC engine.

A cyclone furnace is capable of 5.1e6 kcal\sq m, which was the highest combustion intensity found in power plants until the pulse combustor was tried and a rate 10 times that figure was achieved.

<HTML>Happy New Year Peter,
The best information I can give you is that you search out a copy of the book: "Pulsating Combustion, The Collected Works of F. H. Reynst", Pergamon Press, 1961. A very rare book, and it took me years to find a copy; but absolutely priceless. The only book I ever heard of dealing with the subject. Goes into dozens of uses for it, stationary boilers, locomotives, marine, coal dust burning, all that sort of stuff. All the math and many design parameters and intake valveless designs are thoroughly examined.
There are, or were, many papers on the subject, so look on web sites for: Argus pulse jet engines, pulse jet engines, V-1 pulse jet, pulsating combustion, etc.. I have a large file on the subject.

Graeme is right, the noise is fantastic in a single tube version. However, Reynst does go into push-pull versions that self cancel the pressure waves.
I still have my Dyna-Jet engine from my model airplane days. We got thrown off the field every time we flew the plane. The racket was deafening.

The heat release is, according to the book and some papers I have on the subject, up to 7.5 MBTU per cubic foot.
Starting one is often very tricky, and hard to throttle, if you wanted varying rates of output.
The valve mechanism is also very tricky, reed valves, aero valveless intakes, rotating butterfly valves. and such all have been tried.
The U.S. Navy spent a lot of time working with this engine for pilotless drones after WW-2 and the O.N.R. published some papers.
Also look for insect foggers and movie studio stage foggers, they also used this engine. Big ones too. I still have a 4" dia reed valve/fuel nozzle assembly from one of these.

Try to contact Jim Tangeman, old time SACA member. When I was trying this idea he got interested too and built some steam generators using this.
Finally abandoned the idea because of the necessary length of the assembly and some nasty operating problems; but any Hemholz (Sp?) type resonator will also work in addition to one long tube. It is a matter of designing a resonating chamber, long organ pipe types and also chamber types, think of large police whistles, same idea.

<HTML>I think Iím suffering brain vapor lock.
With this kind of heat rate in such a small area, and combining this with a Lamont, are we talking about a sixty horse steam generator nearly fitting in a five gallon bucket? I have to be missing something in my guesstimation. This could wind up near three lbs. total system weight to the HP. No, that canít be right. I need to go dig out the books before my brain turns to pudding.
In any fashion, all I can say is GO! Peter!
Garry</HTML>

<HTML>Peter,
Thanks for the data. Burn times in a very large power plant with the coal dust fired cyclone furnaces have a very long flame path and think a longer burn time before passing convective tube banks. 5.1 million kilocaries per square meter possible equates t o 2 million BT per square foot of receiving area, my question was more of the burn rate per cubic foot, not per square foot of firebox area. There is a huge difference in these values when going to a 1 cubic foot firebox to a 1000 cubic foot firebox(1X1X1 vs. 10X10X10), may we concentrate on the miniature boiler concept for comparisons.
Great new topic Peter, God bless your tremendous energy in pursueing these things.
By the way some of you might have noticed that the #Replies for each subject no longer accurately represent the actual, JW says he will update the Phorum software soon and may we be patient in this respect---we certainly owe John a lot of respect for this website. If we could all remember that every post we make is a gift of his effort and gift to us, not a right-- it is not an absolute that his website will be available tomorrow.
Thanks so much John for making this gift available to us.

<HTML>Garry,
A long time ago I made a lengthy post on the difference of combustion space to the available amount of heat transfer---in a Lamont surrounded firebox the size of it makes a huge difference as most of the heat is absorbed due to radiation and that is the crux of the matter. It takes an increasing gas ball emitting temperature for a greater amount of heat transfer to take place per square foot of receiving area with the same absolute receiving temperature.. Rather complex stuff to figure out. In the Lamont that Rod and I have built the gas ball temperature is approxametly 2300F and the receiving temperature probably 700F, it is to the fourth power of this temperature differential tht the radiant work is done---the gas ball temperature is after the radiation has taken place as for all intensive purposes it is done at the speed of light, we are not talking about theoretical calorimeter burning temperatures.... maintaining a gas ball temperature just 200F higher @ 2500F would result in a 60% increase in the available energy to be transmitted by radiation per square foot. However the available energy is not the transferred energy, possible only 40-50% would be absorbed due to gas partial pressures, any flame luminosity, receiving surface absorbtivity etc.

When I first came across this topic I checked out the total size needed for the burner and sound insulation for a typical steam car boiler and found it quite large overall. While the combustion volume is very small, the supporting sheetmetal can be big. When looking at any system, you have to examine everything needed and restrictions on fuel type, layout needed, costs, ease of use, safety aspects and the like. I don't remember the critical issues that put it in the "too-hard" basket but there were enough to not even get it into a possible burner list. It is a very interesting burner tho and I would be interested in seeing how compact and quiet the commercial designs ended up.

<HTML>Thank you George and Graeme. I let my imagination run away with me for a bit. The trade offs in engineering are something that always fascinate me, even when my brain short circuits the fundamentals of the art.

If someone can make a pulse burner work, that does self cancel itís own sound waves, it sounds like the gains from reduction in combustion chamber volume size, and perhaps more importantly the major reduction in energy to power this burner, would be parallel blessings for small scale steam generator design.
Ah, well... back to reality :)
Garry</HTML>

<HTML>Andy,
Is that all you could find ? Ha Ha! Thanks for the links and the funny email to Lee. I had to use my corporate decoder ring to read it.

George,
It seems the modern pulse combustor burns at a cool enough temperatutre to prevent the formation of NOx compounds with out our help.

Graeme,
There is no neet to run the pulse combustor in resonance so the size of the burner is not restricted by acoustic properties. This only applies to pot type burners, those with 2 ports must run at the resonant frequency.

John,
The pot burner is not often run at resonance and hemholtz resonation has nothing to do with the operation in most cases.

Jim, I have most of the information from the Pulsating Combustion book in the form of individual papers but I am looking for a copy for a couple years now.

I will get some drawings posted soon with a bit more explination of the parallel operating burners and how they can be setup for silent operation.

I found a lot more links but most were applications of palse combustion to other processes. They didn't really talk about palse combustion burners.

They are sure an interesting idea. But it looks that the burning is confined to such a small space that it would hard to utilize readiant heat to any extent. I suspect that you need at least some minum resonent frequancy to maintain auto ignition. That puts a limit on the combustion chamber size.

Perhaps a small palse combuster could be used to drive a larger burner.